JP-2008-242544A (US-2008/0243389A1) shows a collision detector (warning apparatus) which defines an warning area based on a relative speed between a subject vehicle and an external object and which makes a warning that the subject vehicle is likely to come into contact with the external object when the external object comes into the warning area.
In the above collision detector, if a pedestrian moves at a vicinity of a subject vehicle in a direction which is the same as a direction in which the subject vehicle will start, it is likely that no warning area may be defined in such a manner as to include a position of the pedestrian. Under such a condition, the subject vehicle starts and it can not be determined that a contact between the subject vehicle and the pedestrian will occur until a relative speed therebetween is varied. Thus, it may be too late to output a signal indicating that they may come into contact with each other.
Further, in the above conventional collision detector, it is determined whether the subject vehicle may come into contact with an external object under an assumption that the subject vehicle travels forward in a constant direction. If a direction in which the subject vehicle travels is varied after the subject vehicle stopped, it is likely to incorrectly determine that the subject vehicle may come into contact with the external object.